In the above-identified applications there are described high-speed vehicles for interurban, intraurban and rural-urban transport of passengers and freight. In such systems frictional engagement of a vehicle with a road bed or track can be avoided by the use of levitation principles, i.e., suspending the vehicle magnetically or on an air cushion at some distance from the juxtaposed road bed surface. While principal interest, for the purpose of the present invention, resides in electromagnetic suspension or levitation systems, it should be understood that principally hereof are also applicable to air-suspension systems.
In magnetic levitation systems, the vehicles are suspended by magnetic forces from the track which can be provided on opposite sides with a pair of substantially continuous armature rails.
Each side of the vehicle can be provided with rows of suspension electromagnets and a substantially constant suspension gap is maintained between the cores of the electromagnets and the armature rails by suitable circuitry.
For lateral guidance of the vehicle on the track, the suspension electromagnets and armature rails may be shaped as described in the aforementioned copending application so that the lateral centering forces are produced simultaneously with suspension forces, or additional laterally effective guide eletromagnets and corresponding armature rails may be provided.
Such suspension and guide systems avoid direct contact of the vehicle and the track except for wipers or the like which may be provided to enable the vehicle to pick up electric current from the track.
Similarly it has been attempted to replace the rotary drive motors of conventional vehicles with linear induction motors designed to apply a propelling force to the vehicle without moving parts other than the stator carried by the vehicle body and cooperating with a stationary reaction rail provided on the track. While the present linear induction motor is designed primarily for use with magnetic or other suspension or levitation vehicle systems, it should be noted that the principles here disclosed may be equally applicable to other vehicle drive arrangements.
In general, linear induction motors operate in accordance with eddy-current principles whereby the magnetic field bridging the stator and the reaction rail induces an eddy-current in a conductive layer or part of the rail or in the entire rail. This eddy-current reacts with the magnetic field of the stator and, by causing the field to move along the stator, i.e., by use of a plurality of coils energized in a rotary-field multiface system, a linear force is produced between the stator and the rail which, since the rail is fixed, propels the vehicle along the track.
In the case of a known linear induction motor (see "Elektrotechnische Zeitschrift," edition A, vol. 94, (1973), issue 2, page 97) the stator comprises an annular winding and an associated damping cage and is adapted to be displaced along an elongated stationary flat reaction rail arranged substantially horizontally. The breadth (-width) of the reaction rail of the known linear induction motor is the same as the outer limits of the stator, which limits are formed by two longitudinally extending conductors connecting the individual damping rods of the damping cage with each other. However, it has been found (see Dissertation by Mosebach, "Effekte der endlichen Lange und Breite bei asynchronen Linearmotoren in Kurzstander- und Kurzlauferbauform," Effects of the Finite Length and Breadth in the Case of Asynchronous Linear Motors of the Short Stator and Short Rotor Construction. Technische Universitat Braunschweig, Faculty for Machine Construction and Electrical Engineering, 1972, pages 25 to 29), that transverse forces can occur perpendicularly to the desired advancing forces in the longitudinal direction of the linear induction motor. In the case of a departure from the symmetrical position of the stator in relation to the reaction rail these transverse forces will tend to move the stator further away from said symmetrical position.
As previously noted, a linear induction motor has significant utility for levitation-type vehicles which may be magnetically suspended from and guided along a track. As the vehicle travels along such a track, it is subjected to lateral imbalance forces arising from centrifugal action when the vehicle passes along an arcuate or curved track portion. Wind forces likewise introduce lateral imbalance. If the known linear induction motor is used to drive a hovering or levitation vehicle the above-mentioned transverse forces of the linear induction motor are added to the otherwise existing interfering or disturbing forces in the transverse direction which are produced by the track (centrifugal forces) and by the environment (wind forces).
Such added forces must be compensated for by suitable guiding arrangements provided on the track and/or on the hovering vehicle. Since these guiding arrangements provided on the vehicle should be made as small as possible in order to achieve the highest possible power weight ratio ( -- intrinsic weight in relation to the load) and the lowest possible power consumption of the hovering vehicle, it is desirable to reduce the above mentioned transverse forces.
It is further known (Dissertation by Lang, "Einfluss der Streufelder auf Entwurf und Betriebsverhalten asynchroner Linearmotoren," (The Influence of Stray Fields on the Design and Operational Characteristics of Asynchronous Linear Motors), Technische Universitaet Braunschweig, Faculty for Machine Construction and Electrical Engineering, 1973, pages 88 to 91) to enlarge the breadth of the reaction rail so that it is greater than the overall breadth of the stator which results in a reduction of the undesired edge stray fields. However, an increase in the reaction rail breadth is often not possible owing to constructional reasons in the case of suspended or hovering vehicles, apart from strength problems and higher costs.